Cellular telephones are widely used in motor vehicle environments. The use of traditional hand-held telephones in such environments, however, is often distracting to a driver and hinders the driver""s ability to maneuver in traffic. Hand-held telephones, therefore, increase the risk of accident.
As a result, some motor vehicle and cellular telephone manufacturers have developed systems enabling hands-free telephone operation. Such hands-free telephone systems often employ a microphone that is mounted within the vehicle and is used to pick up speech for telephone communication and voice commands. The microphone in such systems is often coupled to a radio/telephone system located within the vehicle. The radio/telephone system generally comprises a traditional cellular telephone system that is coupled to a vehicle radio in such manner to enable the use of the radio amplifier and speakers for listening to incoming telephone audio. The telephone/radio system also provides power to, and receives electrical voice signals from, the microphone.
In operation, a driver typically presses a button on the radio or on the microphone to establish hands-free use. The driver is then able to listen to a caller""s voice via the radio speakers and speak freely without being required to manipulate or hold a telephone. The driver""s speech is transduced to electrical signals by the microphone, which electrical signals are transferred to the radio/telephone system and then to the caller via the vehicle cellular telephone system.
A number of different microphone assemblies have been developed for such hands-free motor vehicle applications. For example, omnidirectional microphone assemblies have been mounted on interior surfaces of automobiles, typically in two locationsxe2x80x94at a forward, central headliner position and at or near the top of the driver side roof support pillar (A-pillar). By their nature, however, omnidirectional microphones pick up sound from all directions, and thus their performance in motor vehicle applications often suffers due to the numerous non-speaker noise sources in the vehicle, such as, for example, the ventilation system, the defroster, other people speaking, etc.
Directional microphones have also been developed for motor vehicle applications, and can produce significant performance advantages over omnidirectional microphones. A typical prior art directional microphone assembly is illustrated in FIG. 1. A microphone 1 is mounted behind a surface 3, which may form part of a mostly acoustically opaque housing or a mostly acoustically transparent grill cover. The front of the element diaphragm is acoustically coupled through tube 5 and surface inlet 7 to the acoustic pick-up region 9. Similarly, the rear of the diaphragm is acoustically coupled through tube 11 and surface inlet 13 to the acoustic pick-up region 9. Tubes 5 and 11 are narrow, generally cylindrical and substantially resonant over the desired frequency range. Acoustic resistor 15 in tube 11 and the enclosed rear volume 17 behind the diaphragm, form a low-pass filter/delay for sound entering surface hole 13. This delay, along with the dimensions of tubes 5 and 11 and the distance between surface inlets 7 and 13, forms a first-order directional pickup pattern in the pick-up region 9 that is directed along a line from surface inlet 13 to surface inlet 7.
Thus, because of the directivity of the pickup, directional microphones generally require that much greater skill and care be used in positioning the microphone within a motor vehicle in order to achieve the aforementioned performance advantages over omnidirectional microphones. Like omnidirectional microphones, directional microphones have also typically been positioned at a forward central headliner location and at or near the top of the A-pillar in motor vehicle applications. Unlike omnidirectional microphones, however, if a directional microphone is improperly installed in those locations, the performance of the microphone can be adversely affected. Similarly, if a directional microphone designed for those locations is installed in another location for which the microphone is not suited, or if the microphone position is modified by the consumer, the performance may also suffer.
It is desirable, therefore, that a microphone assembly design address these installation concerns to maximize directional microphone performance without requiring that an acoustic expert be involved in the installation of the microphone. In addition, it is also desirable that any such design be adaptable to enable flush mounting with any number of existing surfaces in the vehicle, if the vehicle manufacture requires such mounting for aesthetic reasons.
Consequently, it is an object of the present invention to provide a microphone assembly that can easily and properly be installed at the typical headliner and A-pillar locations as well as any number of other locations in the vehicle, and that can accommodate both left and right drive vehicles.
It is another object of the present invention to provide a microphone assembly that can be easily modified for proper installation at different locations but is not easily disturbed by a consumer.
It is a further object of the present invention to provide a microphone assembly that can easily be adapted for flush mounting with any number of surfaces within the vehicle.
These and other objects of the invention are achieved in a directional microphone assembly having a case and a removable directional microphone module. The case is adapted to mount and lock the module in place thereon in a plurality of different orientations. The directional microphone module is removable from the case and may be re-oriented thereon to accommodate different desired mounting arrangements.
The removable directional microphone module is comprised of a directional microphone element having front and rear inlet ports that are acoustically coupled to front and rear inlet paths, respectively. Sound from a pickup region enters the front and rear inlet paths and is coupled via the front and rear inlet ports to front and rear microphone chambers defined in part by a microphone diaphragm.
In one embodiment, front and rear acoustic plugs are located in the front and rear sound inlet paths. The front and rear acoustic plugs are, for example, made of sintered porous plastic or open cell acoustic foam material. A windscreen made of a cloth or screen material may also be located over the acoustic plugs. The windscreen and acoustic plugs generally operate together to protect against dirt, dust, moisture, etc. and cut down on wind noises.
In another embodiment, the front and rear inlet paths are generally non-cylindrical in shape. The inlet paths are substantially non-resonant in a frequency range of desired sound pickup.
In a further embodiment, the removable directional microphone module includes a housing. The microphone element is mounted in the housing, and the front and rear sound inlet paths are formed in the housing. Recesses in the housing receive the front and rear acoustic plugs such that the front and rear acoustic plugs are located, respectively, in the front and rear inlet paths. The acoustic plugs may, when inserted in the recesses, form portions of a top surface of the housing. A windscreen then may be attached to the top surface of the housing.
In a still further embodiment, the case includes at least one mounting surface and a plurality of index notches. The removable directional microphone module likewise includes at least one index tab. When the module is mounted on the mating surface, the index tab engages one of the index notches, depending on the desired orientation of the microphone. The module is then xe2x80x9clockedxe2x80x9d in the selected orientation, but releasable therefrom. The index notches may, for example, be equally spaced at every 30xc2x0 around the mounting surface, thereby enabling flexible orientation of the microphone within the case. The module is also removable from its mounted relationship with the case to enable re-orientation of the microphone and/or support different mounting arrangements.